1. Field of the Invention
The present invention relates to a lens unit in a camera module of a mobile electronic device and a method for manufacturing a lens unit.
2. Description Related to the Prior Art
There are mobile electronic devices such as mobile phones and mobile personal computers which comprise camera functions. A camera module used in the mobile electronic device is composed of an image sensor for capturing a subject image, a lens unit for forming the subject image on the image sensor, a signal processing circuit for processing an image signal from the image sensor, a flexible wiring substrate for electrically connecting the image sensor and the signal processing circuit, a connector for connecting the camera module to the electronic device and attached to an end of flexible wiring substrate, and a holder for holding these components integrally.
The lens unit comprises two or more lenses and a cylindrical lens holding frame for accommodating and holding each of the lenses (see Japanese Patent Laid-Open Publication No. 2009-282264). At the front end of the lens holding frame, a front surface plate is integrally formed with the lens holding frame. An opening, which is an aperture stop for a first lens, is formed in a center portion of the front surface plate. The first lens is inserted from the rear end of the lens holding frame. A front surface of a flange portion, which is integrally formed around the lens, comes in contact with a back side of the front surface plate, which is formed with the opening, of the lens holding frame. Thereby the position of the first lens is determined. From the second lens and on, the lens comes in contact with the flange portion of the lens which is previously inserted into the lens holding frame. Thus the positions of the lenses are determined in order. After the positioning, each lens is adhered to and held by the lens holding frame.
In this configuration, each lens is incorporated into the lens holding frame, so that the optical axis adjustment of the lens unit is difficult. In the Japanese Patent Laid-Open Publication No. 2009-282264, the first lens is attached from the front end side of the lens holding frame, after the second and subsequent lenses are inserted from the rear end side and held by the lens holding frame as in the conventional lens unit.
In the Japanese Patent Laid-Open Publication No. 2009-282264, the optical axis adjustment is performed by moving the first lens, which has a significant impact on the optical axis adjustment, along a surface which is orthogonal to the optical axis and fixing the first lens to a position for maximizing an MTF, at the time the first lens is adhered to the lens holding frame. Thereby the optical axis adjustment of the lens unit is performed promptly and easily. The manufacturing time of the lens unit is reduced.
It is desirable to reduce the thickness of the lens unit in the camera module incorporated in the mobile electronic device, which is particularly in need of reducing the thickness. It is desired to reduce the thickness of the lens unit in the optical axis direction as much as possible. In the Japanese Patent Laid-Open Publication No. 2009-282264, a disc-like lid formed with an opening, which functions as an aperture stop, at its center is placed on the first lens after the first lens is attached to the lens holding frame. The thickness of the lid hinders the reduction of the thickness of the lens unit. The disclosed lens unit is inadequate for use in the camera module in the mobile electronic device.